Our objective is that of studying the spontaneous rhythmic constriction and dilation of the arterial and venous microcirculation termed vasomotion, and to determine: 1) the nature and origin of the phenomenon; 2) to establish how vasomotion is transmitted in the microvasculature; and 3) to explore the consequences of vasomotion for flow regulation and exchange. Our hypothesis is that vasomotion is in part, controlled by the myogenic properties of the microvasculature. We will test this hypothesis by studying vasomotion in the microcirculation of the hamster skin fold window preparation, where the ambient pressure of the animal is varied relative to that of the chamber. The chamber in the rat will be studied in order to observe subcutaneous muscle. The rabbit tenuissimus muscle will also be implemented since this preparation allows for the direct manipulation of input and output vessels, although it must be studied in an acute condition and during anesthesia. Measurements will include the dynamics of diameter changes, the characterization of the chamber vascular anatomy, blood flow in the microvessels and the direct measurement of pressure in the microvasculature along the continuous pathway of A1, A2, A3, and A4 sequence of branching. Vasomotion will be quantitated by a method called Prony Spectral Line Estimator to obtain data on amplitude, frequency, and phase. This will be utilized to measure the speed of propagation of the vasomotion waves, and whether they originate at specific foci that have the function of microvascular pacemakers. Studies will be extended to include the venous microcirculation. The speed of propagation of vasomotion will be compared to that of vasoconstrictor responses that are locally induced through the application of norepinephrine. The effects of vasomotion will be studied in terms of histograms of capillary flow in order to establish how vasomotion affects tissue perfusion. The effects on fluid exchange will be determined by relating the locally measured average capillary pressure to the colloid osmotic pressure of blood, to determine the difference in fluid balance between the active and inactive microcirculation. The hypothesis that pulsatile pressure influences vasomotion will be tested experimentally. This research finds application in the interpretation of whole organ experiments and the analysis of peripheral vascular resistance. The results of these kind of studies are significant to the understanding of hypertension, ischemia, and edema formation.